1. Field of the Invention
The present invention relates to engine analyzer apparatus used for testing internal combustion engines.
2. Description of the Prior Art
One common type of engine analyzer apparatus used for testing an internal combustion engine employs a cathode ray tube having a display screen on which analog waveforms are displayed which are associated with operation of the engine. In a typical apparatus of this type, a substantially horizontal trace is produced on the screen of the cathode ray tube by applying a sawtooth ramp voltage between the horizontal deflection plates of the tube while the analog signal being measured is applied to the vertical deflection plates of the tube. The typical analog signals which are applied to the vertical plates of the cathode ray tube are the primary voltage which exists across the primary winding of the ignition coil, and a signal representative of the secondary voltage of the ignition coil. These voltages are affected by the condition of various elements of the ignition system of the engine, such as the spark plugs.
In the case of a multicylinder internal combustion engine, the primary and secondary voltage waveforms have typically been displayed on the cathode ray tube in one of two ways. In one case, the waveform being displayed represents a complete cycle of the engine, in which the conditions associated with the various cylinders are displayed sequentially in a predetermined pattern. This type of display has commonly been referred to as a "parade" pattern or display.
In the other common method of displaying waveforms, there are a plurality of horizontal traces, one above the other, with each trace being associated with the operation of one of the cylinders of the engine. The number of horizontal traces usually corresponds to the number of cylinders on the engine. This method of displaying waveforms has been referred to in the industry as a "raster" display.
With the advent of low cost microelectronic devices, and in particular microprocessors, digital electronic systems have found increasing use in a wide variety of applications. Digital electronic systems have many significant advantages over analog systems, including increased ability to analyze and store data, higher accuracy, greater flexibility in design and application, and the ability to interface with computers having larger and more sophisticated data processing and storage capabilities. In the past, some engine analyzer systems have been proposed which utilize microprocessors and digital circuitry to control some of the functions of the engine analyzer apparatus. In these prior art systems, however, the waveform display function of the engine analyzer apparatus has remained essentially an analog electrical function, even when the systems utilize microprocessors and digital electronics for other functions.